The invention relates to a new process for producing a surface compound between a substrate and a reactive species.
The processes essentially employed for producing such compounds are anodic treatments or thermal treatments; these treatments have a number of difficulties. Thus in the anodic treatments, the specie present in the electrolytic bath may become incorporated in the grown anodic layer. This may result in many drawbacks such as the early destruction of the dielectric layer, dielectric losses due to ionic polarizations etc. In the particular case of anodic oxidation, oxide growth can occur by the transport of oxygen and cations. The transport numbers are termed respectively anionic (t.sup.-), cationic (t.sup.+), and (t.sup.+ +t.sup.-)=1, the fractions of current transported respectively by these mobile positive and negative charge carriers during the growth. These numbers depend on the experimental conditions and on the nature of the oxidized substance. Dependent on their value are the particular properties of the oxide and the substrate oxide interface; thus for (t.sup.+ =1), the oxide being formed can come away from the substrate. Moreover, in the case of a substrate of formula A.sub.x B.sub.y, gallium arsenide for example, the transport numbers t.sub.A.sup.+ and t.sub.B.sup.+ may be different. Consequently, one of the two specie A or B may accumulate at the substrate insulating interface and create a more or less extended zone of poorly defined properties. In the thermal treatments in which the body to be treated is immersed in a suitable liquid, the active fluid must be clean otherwise certain impurities may be incorporated in the layer in the course of growth and, lastly, the substrate must be stable at the treating temperature.
An object of the invention is to provide a process whereby these drawbacks are at least partially avoided.